Most balloons used in dilatation catheters are designed to provide a uniform and controllable diameter over the length of the balloon. Typically, the dilatation balloon does not conform to the curved shape of a blood vessel during inflation of the balloon. The body of the balloon becomes straight and rigid as the balloon is inflated under pressure of an inflation liquid introduced through an inflation lumen communicating between the balloon and the proximal end of the catheter. Consequently, when inflated, the balloon tends to straighten the blood vessel at the site of the lesion. That is not desirable because the dilatation balloon may not effectively open the blood vessel or may cause additional damage to the blood vessel walls as a result of the straightening.
Additionally, when inflated, the dilatation balloon blocks blood flow through the blood vessel, thus limiting the length of time that the blood vessel may be dilated before chest pain requires the dilatation balloon to be deflated. Longer dilation times are desirable because conditions such as restenosis may tend to occur less frequently when longer dilation times are used.
Upon deflation, a dilatation balloon may contract in a manner that forms "wings." That is, rather than maintaining a circular cross-section upon deflation, the dilatation balloon deflates to form flat portions called wings that extend radially outward from the balloon. This so-called "winging" phenomenon is undesirable because it results in a larger crossing profile when locating the balloon in a stenosis.
Some dilatation balloons are designed to have diametrical compliance, that is, a change in diameter of the dilatation balloon as a function of inflation pressure. Dilatation balloon materials and designs are generally chosen to provide linear diametrical compliance, that is, a linear relationship between dilatation balloon diameter and inflation pressure. Typically, diametrical compliance is achieved by selecting a material for the balloon that stretches upon application of inflation pressure. However, conventional compliant dilatation balloons have no maximum size limitation and as a result increased inflation pressures cause the balloon to keep expanding, thereby risking injury to the blood vessel if overinflated.
It would be desirable, therefore, to provide dilatation balloons that avoid the foregoing difficulties.